Alzheimer's disease (AD) is the most common cause of dementia, afflicting millions of people including the aging populations of veterans. It is extremely important and urgent to find pathophysiological basis and potential treatment for this devastating disease. AD has two prominent features: (1) a selective loss of basal forebrain (BF) cholinergic neurons and cholinergic deficits in cortical areas that lead to cognitive impairment; (2) the accumulation and aggregation of excessive ?-amyloid peptides (A?), which triggers a complex cascade that leads to synaptic alterations and neural injury. Our goal of this proposal is to understand how BF cholinergic neurons are selectively degenerated in AD, and whether it is triggered by A?. BF receives intensive glutamatergic inputs, and BF cholinergic neurons are particularly vulnerable to glutamate excitotoxicity from overactivation of NMDA receptors. One of the metabotropic glutamate receptors, mGluR7, displays a remarkably low affinity for glutamate, thus has been suggested to serve as an emergency receptor to inhibit glutamatergic transmission under pathophysiological conditions. We hypothesize that activation of mGluR7 causes the suppression of NMDAR responses in BF, and A? selectively disrupts mGluR7 inhibition of NMDAR signaling in BF cholinergic neurons. Consequently, the mGluR7-mediated protection against NMDA excitotoxicity is abrogated by A? selectively in BF cholinergic neurons. To test this hypothesis, we will use the combined electrophysiological, pharmacological, biochemical and molecular biological approaches to address two specific aims: (1) To study mGluR7 regulation of NMDAR trafficking & function in BF and the underlying mechanism. (2) To study A?-induced selective impairment of mGluR7 effects on NMDARs in BF cholinergic neurons and the underlying mechanism. Knowledge gained from this study will provide important information linking several key components critically involved in the pathophysiology of AD, including acetylcholine system, A? and NMDA receptors. Not only will it offer significant insights into the cellular and molecular basis of AD, particularly the potential mechanism for the selective vulnerability of BF cholinergic neurons in AD, but also it will help identify new therapeutic targes for AD treatment, such as mGluR7 and regulators of cytoskeleton dynamics involved in mGluR7 signaling.